Hey girls -- It was actually really easy since there was just one groomsman and my DH. The groomsman apparently owns a lot of suits and likes to dress up, and he had coincidentally just purchased a khaki suit from Kohl's. He showed it to DH and DH liked it a lot. The price was right, too, so DH ordered it and Ta-Da! Very simple.
But....if he hadn't already owned it, DH and I would have just picked one out and asked him to buy it (within a reasonable price range, of course).